The present invention relates to digitizing tablets, and the like, and, more particularly, to an electronic pen for a digitizer capable of providing signals to a computer for pen movement in three dimensions relative to a planar tablet comprising, a hollow, pen-shaped body member having a writing tip end; sensing means disposed in the body member adjacent the writing tip end and having wires thereof connectable to the computer for use in developing X- and Y-axis positional signals relative to movement of the writing tip end over the surface of the tablet; a pen member disposed in the body member for longitudinal slidable movement within the body member, the pen member having a writing tip passing out through the body member at the writing tip end and an opposite inner end; linear position transducer means disposed within the body member for producing on output wires therefrom connected to the computer Z-axis positional signals relative to the pressing of the writing tip end against the surface of the tablet; means for indicating a first Z-axis positional signal as the starting point of a range of movement; and, means for indicating a second Z-axis positional signal as the ending point of a range of movement.
Digitizing systems are gaining popularity in the computer art as a means of inputting positional data to a computer, or the like. While digitizing systems were originally large and expensive, as were the computers with which they were used, many smaller and inexpensive digitizing systems are now available for use with the smaller "personal computers" that are available for both home and business use. Of these digitizing systems, the digitizing tablet is, probably, the most popular. As depicted in FIG. 1, a basic digitizing tablet system, such as that generally indicated as 10, comprises a tablet 12 and an electronic pen 14. Both the tablet 12 and the pen 14 are connected to the computer (not shown) by wires 16 and 18, respectively. For simplicity, only two wires are shown with respect to 16 and 18 in each case. This is representative only and more wires are probably actually interconnected to the computer, depending on the type of system being implemented and the features provided.
As shown in FIG. 2, the pen 14 for such a 2-dimensional system typically comprises a hollow, plastic, cylindrical, body 20 with a coil 22 disposed adjacent the "writing" end of the body 20 and connected to the wires 18. As the pen 14 is moved over the surface of the tablet 12, the 2-dimensional X,Y coordinates of its position are provided to the computer over the wires 16, 18 by electronic means involving the coil 22 which are not important to the present invention and, therefore, omitted in the interest of simplicity. To provide the user with a means of signaling the computer when the writing tip of the pen 14 is at a desired coordinate point, a switch is normally provided on the pen 14 and connected to the wires 18. Sometimes, the switch is mounted to be activated by finger pressure. More often, however, the construction is a shown in FIG. 2 wherein there is a longitudinally slidable, plastic, pen member 24 having a "writing tip" 26 which passes through the coil 22 and extends out of the pen body 20. At a desired point, the pen body 20 is pressed towards the surface of the tablet 12 causing the pen member 24 to move longitudinally into the pen body 20 and activate the bistable switch 28 disposed therein. When the longitudinal inward pressure on the pen member 24 is released, the switch 28 returns to its normal position. For those interested, attention is directed to U.S. Pat. No. 4,532,376 entitled ELECTRONIC PEN WITH SWITCHING MECHANISM FOR SELECTIVELY PROVIDING TACTILE OR NON-TACTILE FEEL by Lynn H. Rockwell and assigned to the common assignee of this application. A more detailed description of the construction of an electronic pen for 2-dimensional digitizing as described above is provided therein.
As depicted by the drawing of FIG. 3, there are instances in the prior art where signals related to three dimensions are desirable; that is, the providing of a signal related to the amount of longitudinal pressure on the pen member 24 in addition to its X,Y position on the surface of the tablet 12. For example, when using so-called "painting" software, area color or shading can be dynamically set through sensing the pressure on the pen member 24 as a function of its longitudinal displacement. To date, prior art attempts at providing an electronic pen capable of providing a signal in the Z-axis (i.e. generally perpendicular to the tablet) have been limited to complex electronic detection of the longitudinal movement of the pen member 24. Such a prior art approach is shown in simplified form in FIG. 4 wherein the pen 14' is shown in a general form. Again, there is a hollow body 20 having an annular coil 22 and a longitudinally sliding pen member 24 with its writing tip 26 passing through the coil 22 and extending out of the body 20. The pen member 24 is biased to its most extended position by a coil spring 30 disposed between an inner ridge 32 within the body 20 and a collar 34 on the pen member 24. The inner end 36 of the pen member 24 is disposed to interact with a linear position transducer 38 which is operably connected to provide a sensible signal to the computer (not shown) over the wires 18. In one prior art system, the linear position transducer 38 comprises a magnet carried by the pen member 24 and used to modify the characteristics of a transistor as a function of proximity through the use of the so-called Hall effect. In another prior art system, annular coils are disposed within the body of the pen body 20 and a core is carried by the end of the pen member 24 to move through the coils and, thereby, modify their electronic characteristics. As can be appreciated, both these prior art methods are complex and difficult to build into a pen and in their operation. Typically, a special pen body must be constructed to accept all the components required to provide the Z-axis signal according to these prior art techniques.
Wherefore, it is the object of the present invention to provide an electronic pen for use with digitizing tablets, and the like, providing not only X,Y positional signal inputs; but, additionally, a Z-axis signal reflecting pressure on a longitudinally movable pen member or, alternatively, longitudinal displacement of the pen member wherein the sensing apparatus developing the Z-axis signal is simple to operate and interface with and is simple and easy to incorporate into a standard electronic pen body.
Other objects and benefits of the present invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.